Turbocharged Direct Injection

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Turbo Direct Injection (TDI) is the technology used for modern Diesel engines produced by Volkswagen Group, and is widely used in passenger cars produced by the company (especially those sold in Europe).

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[edit] Overview

The engine uses direct injection where a fuel injector sprays directly into the engine cylinder rather than the pre-combustion chamber prevalent in older diesels which used indirect injection. The engine is coupled with a turbocharger and intercooler to increase the amount of air that can get into the engine cylinders, thereby increasing the amount of fuel that can be injected and combusted. In combination, these allow for greater engine performance while also decreasing harmful emissions.

Other companies also use similar technology today, but "TDI" usually refers to the engines used in cars made by Volkswagen, Audi, and related brands. Normally-aspirated engines (those without a turbocharger) made by Volkswagen Group use the label "Saugdiesel Direct Injection" (SDI).

The reduced material volume of the direct injection diesel engine reduces heat losses and thereby increases engine efficiency, at the expense of increased combustion noise. A direct injection engine is also easier to start when cold, due to the reduced heat loss of the design.

[edit] History

The first TDI engine was a 2.5L inline five-cylinder introduced in the Audi 100 in 1989. Over time, the TDI arrangement has been enhanced by improving the efficiency of the turbocharger, increasing the pressure at which fuel can be injected, and more precisely timing when the injection of fuel takes place. There have been a few major generations, starting with what are known as "VE" engines. In 2000, the Pumpe Düse (PD, variously translated "pump nozzle", "unit injector", "pump injector") engine began to appear in Europe, eventually coming to North America a few years later.

The PD design was a reaction to the development of common rail fuel injection by competitors; an attempt by Volkswagen to create an in-house technology of comparable performance that would not require any royalties to be paid. However, while Pumpe Düse engines had a significantly higher injection pressure than older engines, they couldn't keep up with common rail and weren't able to control injection timing as precisely (a major factor in improving emissions). PD technology was abandoned, and new engines appearing as of 2006 are using the common rail technique with piezoelectric injectors.

A racing version of the common rail TDI engine made an impact in 2006 when it was used in the Audi R10, which won the 12 Hours of Sebring and 24 Hours of Le Mans, becoming the first diesel-powered car to win either of those races. Fuel economy was a significant factor, as the car didn't have to refuel as often as others in the race. The car used a special synthetic diesel blend as fuel.

TDI engines are frequent winners of various prizes in the International Engine of the Year Awards. In 1999 in particular, 6 out of 12 categories were won by TDI engines: 3 were Volkswagen, 2 were BMW and 1 Audi. Its worth noting, that year, the Volkswagen 1.2L TDI beat the Toyota Prius to win "Best Fuel Economy".

[edit] Fuel

Like all diesel engines, TDI engines can run on petrodiesel or biodiesel. When converted properly, one can be made to also run on straight vegetable oil (SVO) or waste vegetable oil (WVO). Most conversions also make it possible to run on kerosene.

In terms of fuel efficiency, and clean emissions when run on biodiesel or SVO/WVO, TDI engines are among the best on the market. This is often overlooked because they do not drive on gasoline. The common Volkswagen 1.9L TDI, officially gets between 37-57 mpg for the automatic and 42-61 mpg for the 5-speed.

Newer TDI engines, with higher injection pressures, are less forgiving about poor-quality fuel than their 1980s ancestors. No. 2 diesel fuel is recommended since it has a higher cetane number than No. 1 fuel and has lower viscosity (better ability to flow) than heavier fuel oils. Many environmentalists have converted their TDI cars to run on SVO or WVO by installing devices that pre-heat the oil to lower its viscosity, as the viscosity of unrefined oil is much higher than petrodiesel or biodiesel.

Volkswagen of America does not endorse the use of biodiesel in high percentages and states that "[s]hould the use of substandard fuels, or higher level blends of biodiesel, damage your engine or fuel system, such damage cannot be covered under warranty." Thus a high-percentage biodiesel user who encounters fuel system problems can reasonably expect difficulty obtaining service under warranty if the biodiesel use is apparent to the dealer.

[edit] See also

[edit] External links

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